1. Field of the Invention
The present invention relates generally to multi-node sensor systems. More specifically, the present invention relates to a system, sensor nodes, program product, and related methods to monitor the health of structural components and to deliver power to distributed sensor nodes.
2. Description of the Related Art
Various types of platforms such as, for example, aircraft structural components, aircraft skins, or other related components, when in operation are subjected to various environmental conditions such as stress and strain, exposure to temperature extremes, and/or significant vibration energy. Due to the various environmental conditions such components can suffer material degradation over time.
Structural health monitoring helps promote realization of the full potential of such components. Remotely position sensors (nodes) have been installed adjacent to such structures/components to monitor various parameters such as, for example, strain levels, stress, temperature, pressure, or vibration level to help manage physical inspection schedules, maintenance schedules, to help predict material failure, and generally monitor the “health” of such components. Such sensors have been provided a dedicated power supply such as power obtained through conductors, e.g., wires, connected to the aircraft electrical system or through chemical batteries. Such wiring can undesirably result in increased weight and complexity of the component being monitored and/or the associated structure, and are subject to damage or breakage requiring extensive repair costs and down time. Depending upon available space, batteries can be inappropriate due to their size. Batteries can also have a limited service life and, therefore, typically require periodic inspection and/or replacement, are often positioned in locations difficult to reach, and often require costly disassembly and reassembly of the sensor or component to perform service on the battery. Further, batteries may not be suitable due to environmental constraints, i.e., temperature changes often affect battery performance.
Some more recent structural health monitoring systems include sensors connected to a network of fiber-optic conductors to form an interrogation system. Such fiber-optic conductors, as with electrical conductors, can significantly raise the complexity of the component and/or deployment the sensor system. Other structural health monitoring systems include self-powered sensors attached to or embedded within the components to be monitored that can reduce dependence on batteries or any other external power source. Such sensors can be relatively small in size and can utilize the energy translated through the component being monitored as a power source. Such devices can include those known as micro-electro-mechanical systems (MEMS). This type of sensor can typically consume very low amounts of power in the microwatt range. Such devices can include those known as piezoelectric devices. Some related piezoelectric devices can be in the form of actuators which can to apply a force on the associated structure to dampen detected vibrations. That is, such actuators can selectively inject directed vibrations to cancel existing undesired vibrations or noise.
Both of the foregoing example types of sensors can generate small electrical currents when, for example, the material is deflected, such as when the monitored component vibrates. Further, both of these types of sensors can include a storage element such as a capacitor to supplement power requirements. Such devices, however, must be positioned in both those areas having a high level of environmental energy and also in areas having a low level of environmental energy to provide sufficient monitoring capability. Because power harvesting relies on energy being available in the vicinity of the power harvesting portion of the sensor, even with the inclusion of a separate storage element, the sensors positioned in the areas of low environmental energy often do not receive sufficient power to provide continuous sensing capability necessary to perform even sampled sensing having a small duty cycle. Correspondingly, such environmental energy limitation often imposes a constraint on where the sensors can be located and thus, the adequacy of using such sensors. Additionally, the available energy distribution may change such that an area once having a high level of environmental energy now is subject only to a low-level of such energy, making power availability less reliable.
Still other health monitoring systems include wireless sensors that receive energy to retrieve sensed data from, for example, a mobile vehicle or to handheld base device which transmits a signal to each wireless sensor positioned on or in the monitored component or structure, to power or recharge the sensors. Typically an operator positions the base device adjacent the various sensors to power the sensors to thereby receive sensor data. With respect to a moving structure, however, such as, for example, an aircraft or other vehicle in operation, this type of device does not provide power to sensors that utilize a near field communication scheme.
In view of the foregoing, it would be desirable to provide a self-powered sensor system that reduces dependence on batteries or any other external power source that can include sensors capable of harvesting energy from areas of high environmental energy and provide power to those sensors in areas of low environmental energy.